Free lift cylinder



J. E. OLSON FREE LIFT CYLINDER Jan. 8, 1963 5 Sheets-Sheet 1 Original Filed March 17, 1958 FlG.2

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INVENTOR. JOHN E. OLSON BUGKHORN, CHEATHAM & BLORE ATTORNEYS Jan. 8, 1963 J. E. OLSON FREE LIFT CYLINDER 3 Sheets-Sheet 2 Original Filed March 17, 1958 INVENTOR. JOHN E. OLSON BY BUCKHORN,CHEATHAM& BLORE A TTOPNEKS Jan. 8, 1963 J. E. OLSON FREE LIFT CYLINDER 5 Sheets-Sheet 3 Original Filed March 17, 1958 BY BUCKHORN, CHEATHAM &BLORE A TTORNEYS 7 1 ii i 8 glllfllllllll'lllllllllll"llI'll!!! r mqllv'liflrli l/l/ Ill/l/ll/lll fill/Ill! 1.. I II. I

3,072,219 Patented Jan. 8, 1963 (ice 7 Claims. (Cl. 1879) This invention relates to industrial free lift trucks and particularly to the free lift assemblies or units of such trucks. The present application is a continuation of my prior application entitled Free Lift Cylinder, Serial No. 722,092, filed March 17, 1958, now abandoned; which was a continuation-in-part of my prior application entitled Free Lift Truck, Serial No. 543,822, filed October 31, 1955, now Patent 2,915,144. The free lift cylinder unit disclosed and claimed in the present application is basicaly shown in my prior application, Serial No. 543,- 822. However, in the latter application it is associated with a special upright structure, while here it is associated with a conventional upright structure.

A free lift cylinder unit is so designed that upon movement of one of the cylinders the load carriage of the truck may be elevated without extending the uprights. Thereafter, the uprights may be extended and the carriage elevated.

Heretofore, the cylinder assemblies have been very complicated, requiring numerous parts, and there has been a constant demand for simplification of these units since inherently they are expensive because of the close tolerances that must be held and because of the extensive machine work that must be performed.

It is a main object of the present invention to provide a free lift cylinder unit which is considerably simpler than prior units and considerably less expensive.

A more particular object of the invention is to provide a free lift cylinder unit including only three cylinders, wherein two of the cylinders are much shorter than the third cylinder, and yet the cylinder unit is capable of moving a load carriage and extending the uprights in the same manner as is possible with more complicated cylinder units having more cylinders, or longer cylinders.

Various other objects of the invention will be apparent from the following description taken in connection with the accompanying drawings wherein:

FIG. 1 is a front View of an upright structure mounted on a lift truck and incorporating a free lift cylinder unit of the present invention;

FIG. 2 is a side elevational view of the upright structure, parts being broken away for convenience in illustration;

FIG. 3 is a vertical sectional view of the cylinder unit showing the same in its inoperative or rest position;

FIG. 4 is a horizontal section taken along line 4-4 of FIG. 3;

FIG. 5 is a somewhat diagrammatic sectional view in side elevation also showing the cylinder unit in its rest or inoperative position;

FIG. 6 is a view similar to FIG. 5 but showing the cylinder unit after it has completed its free lift movement; and

FIG. 7 is a view similar to FIG. 6 but showing a subsequent stage of the operation.

Referring to thte accompanying drawings and particularly to FIGS 1 and 2, the truck 11, which is only diagrammatically disclosed, has a conventional extensible upright structure mounted on the front thereof comprising a pair of spaced connected outer uprights pivoted on the truck frame and forming a fixed outer upright structure 13, and a pair of spaced connected inner uprights forming an inner movable upright structure 15 guided for vertical movement in a conventional manner, not shown, by the outer upright structure. A load carriage 17 is mounted on the inner upright structure for movement relative thereto in a conventional manner not necessary to disclose. A free lift cylinder unit generally entitled 19 of the present invention is adapted to raise the load carriage 17 through the medium of chains 21 along the length of the inner upright structure 15 without extending the upright structure, and then to move the load carriage and the inner upright structure upwardly together.

Referring to FIGS. 1, 2 and 3, the cylinder unit 19 includes an inner cylinder 31 constituting a plunger and connected at its lower end to a crossbrace 33 of the outer upright structure 13. Surrounding the upper portion of the plunger 31 and slidably engaging the plunger is an intermediate cylinder 35, and surrounding the intermediate cylinder and slidably engaging the same is an outer cylinder 3-7. The upper end of the outer cylinder 37 is closed by a cap 38 which is connected by a bracket structure 39 to a crossbrace 40 connecting the upper ends of the inner uprights, as best shown in FIG. 1.

The lower end of the intermediate cylinder 65 projects out of the outer cylinder 37 and carries a crosshead 51 supporting a pair of sheaves 53. A larger pair of sheaves 55 is mounted on the bracket structure 39 and, thus, is in effect carried by the inner upright structure 15. The chains 21 are connected at one set of ends to a flange 57 formed on the cap 38, as is best shown in FIGS. 1 and 2, and then are trained downwardly and passed under the lower sheaves 53' and then upwardly over the upper sheaves 55 and then downwardly again past the lower sheaves and are anchored at 56 to the load carriage 17 as best shown in FIG. 2.

The parts of the cylinder unit are so dimensioned that, as will be presently explained, fiuid pressure entering the cylinder unit will first force the intermediate cylinder 35 downwardly to move the sheaves 53 downwardly relative to the sheaves 55. Because there are two runs of the chains that are in effect lengthened because of the separation of the lower sheaves 53 and the upper sheaves 55, as clearly apparent from FIG. 2, the carriage 17 will be raised at twice the speed of the crosshead.

At approximately the time that the load carriage reaches the upper end of the inner upright structure 15, the intermediate cylinder 35 has reached its bottom-most limit of travel and thereafter, the outer cylinder will move upwardly carrying the intermediate cylinder with it and also raise the inner upright structure and the load carriage upwardly together at a one-to-one rate.

Now, turning to the specific structure of the cylinder unit and referring particularly to FIGS. 3 and 4, the crosshead 51 carries a suitable packing assembly 71 slidably engaging the exterior of the plunger 31. The plunger carries three pads 73 at its upper end slidably engaging the inner surface of intermediate cylinder 35. These pads are disposed in spaced relation around the plunger and in interdigitated relation with respect to three pads 75 provided on the inner surface of the upper end of the intermediate cylinder 35. These pads are for guiding purposes as will be presently apparent.

The upper end of the intermediate cylinder 35 also carries a packing assembly 77 slidably engaging the inner surface of the outer cylinder 37, and the lower end of the outer cylinder 37 carries a guide bushing 78 and a wiper 79 which slidably engage the outer surface of the intermediate cylinder 35. A shoulder 80 below the packing of the assembly 77 and a shoulder 81 surrounding the bushing 78 serve as stops as will be presently apparent.

The upper end of the plunger 31 is provided with a plug 85 having a pilot portion 87 slidably projecting into a bore formed in the cap 38. This pilot portion 87 serves as a guide as will be presently apparent, and has its upper end tapered to readily enter the bore in the cap.

As clearly shown in FIG. 3, there is a port 91 formed in the plunger 31 just below the plug 85 to place the interior of the plunger in communication with the annular space between the outer surface of the plunger and the inner surface of the intermediate cylinder 35.

It is here pointed out that the effective area of the intermediate cylinder is equal to the area of the interior of the outer cylinder minus the area of the exterior of the plunger. The reason for this is that the intermediate cylinder has an outer packing assembly 77 slidably engaging the interior of the outer cylinder and a second packing assembly 71 engaging the exterior of the plunger 31.

In order that the intermediate cylinder be the first cylinder to move, its effective area multiplied by the mechanical advantage provided by the chains 21 must be greater than the area of the plunger. That is to say, in the form of the invention disclosed, when the intermediate cylinder moves downwardly the load carriage is moved upwardly at twice the speed of the intermediate cylinder. However, the outer cylinder can move upwardly together with the intermediate cylinder to raise the load carriage at a one-to-one ratio. The force urging this movement is equal to the area of the plunger multiplied by the unit fluid pressure. Thus to make certain that the intermediate cylinder moves downwardly first, its effective area must be more than twice the area of the plunger 31. Of course, if the mechanical advantage of the chain arrangement were one-third, instead of onehalf, the effective area of the intermediate cylinder would have to be more than three times the area of the plunger in order to achieve downward movement of the intermediate cylinder rather than simultaneous upward movement of the intermediate cylinder and the outer cylinder.

Referring to FIGS. 3, 4 and 5, upon the application of fluid pressure to the interior of the plunger through a port 92 in the lower end thereof, the fluid passing through the port 91 into the annular space between the plunger and the intermediate cylinder and also passing upwardly between the pads 73 and 75, suitable space being provided between the pads to allow this so that this fluid is applied against the packing 77 as well as against the packing 71. Thus, the intermediate cylinder moves downwardly raising the load carriage 17 at a two-to-one rate.

During such downward movement, the pads 75 on the intermediate cylinder move downwardly relative to the pads 73, as shown in FIG. 6, and the pads 75 function to guide the upper end of the intermediate cylinder and maintain it in a predetermined spaced relation relative to the plunger. Also during the downward movement of the intermediate cylinder the pilot plug 85 maintains the upper ends of the outer cylinder and the plunger in proper concentric relation relative to one another.

Just as the load carriage reaches the upper end of the inner upright structure, the shoulder 80 on the intermediate cylinder engages the shoulder 81 on the outer cylinder to limit further downward movement of the intermediate cylinder. Thereafter, the continued application of fluid pressure causes the outer cylinder to move upwardly to raise the inner upright structure, the load carriage and also the intermediate cylinder 35. During such upward movement, the pads 75 will pass by the pads 73 and move upwardly therebeyond until the crosshead 51 engages the pads 73. The chains 21 function to hold the intermediate cylinder 35 against any substantial turning movement relative to the plunger 31 when the pads 73 and 75 are separated, so as to maintain a desired orientation of the pads relative to one another.

When the fluid pressure is relieved, the reverse operation takes place. It is here pointed out that the fit of the pilot portion 87 within the cap 38 is rather close so that fluid within the cap is slowly expelled therefrom. Thus the carriage and the inner upright may be dropped swiftly, but they are cushioned at the end of the inner upright travel by the the cooperation of the pilot portion 87 and the cap 38.

The present invention provides a free lift cylinder unit having only three cylinders, only one of which is full length and the other two are approximately half length, in the particular upright structure disclosed. Thus this cylinder unit requires considerably less machining work than prior free lift assemblies which have longer cylinders or more cylinders. Also this cylinder weighs less than prior free lift cylinders, and since the cylinder is disposed forwardly of the front axle of the truck and thus tends to tilt the truck forwardly, less counterweight at the rear of the truck is required.

While the invention has been explained with a simple upright structure, that is, a fixed upright structure and a single movable upright structure, the invention is applicable to more complicated upright structures including third and fourth upright structures.

Having described the invention in what is considered to be the preferred embodiment thereof, it is desired that it be understood that the invention is not to be limited other than by the provisions of the following claims.

I claim:

1. A mast assembly comprising an extensible upright structure, a load carriage movably engaging said structure, a compound cylinder unit including an inner cylinder constituting a plunger, an intermediate cylinder and an outer cylinder, said intermediate cylinder being shorter than said inner cylinder and movable downwardly upon the application of fluid pressure to said cylinder unit, means connecting said intermediate cylinder to the load carriage to elevate the load carriage without extending the upright structure, said outer cylinder being subsequently movable upwardly upon continued application of pressure to raise the carriage and extend the upright structure, said plunger having guide portions at its upper end slidably engaging the interior of said intermediate cylinder, said intermediate cylinder having guide portions at its upper end slidably engaging the exterior of said plunger, the first and second mentioned guide portions being arranged to by-pass one another during relative movement between said intermediate cylinder and said plunger.

2. A compound cylinder unit for a mast assembly of the type having an extensible upright structure and a load carriage movably engaging said structure, said unit comprising an inner cylinder constituting a plunger, an intermediate cylinder and an outer cylinder, said intermediate cylinder being shorter than said inner cylinder and movable downwardly upon the application of fluid pressure to said cylinder unit, means connecting said intermediate cylinder to the load carriage to elevate the load carriage without extending the upright structure, said outer cylinder being subsequently movable upwardly upon continued application of pressure to raise the carriage and extend the upright structure, said plunger having guide portions at its upper end slidably engaging the interior of said intermediate cylinder, said intermediate cylinder having guide portions at its upper end slidably engaging the exterior of said plunger, the first and second mentioned guide portions being offset from one another so as to bypass one another during relative movement between said intermediate cylinder and said plunger.

3. A compound cylinder unit including an inner cylinder constituting a plunger, an intermediate cylinder and an outer cylinder, said intermediate cylinder being shorter than said inner cylinder and movable downwardly upon the application of fluid pressure to said cylinder unit, means for connecting said intermediate cylinder to a load carriage to elevate the load carriage without extending the upright structure guiding said carriage, said outer cylinder being subsequently movable upwardly upon continued application of pressure to raise the carriage and extend the upright structure, said intermediate cylinder having packing at its lower end slidably engaging said plunger and packing on its upper end slidably engaging said outer cylinder so that said intermediate cylinder is ejected from said outer cylinder in plunger-like fashion with the fluid pressure acting on the area of the annulus between the exterior of the plunger and the interior of the outer cylinder, and guide means at the upper end of the intermediate cylinder for establishing a guided fit be tween the upper end of the intermediate cylinder and the plunger.

4. A compound cylinder unit for an industrial lift truck, said unit including an inner cylinder constituting a plunger, an intermediate cylinder surrounding said plunger at the upper portion thereof in the contracted position of said compound cylinder, said intermediate cylinder being shorter than said plunger and being open at its opposite ends, an outer cylinder surrounding said inter-mediate cylinder and having a closed upper end above the upper ends of the plunger and intermediate cylinder, said intermediate cylinder having means projecting below the lower end of said outer cylinder for supporting reeving means, said plunger having a closed upper end but having port means adjacent its upper end for the flow of fluid therethrough, means at the upper end of said plunger having a sliding guided fit with the upper end of said outer cylinder to hold the upper ends of said plunger and outer cylinder in concentric relation when said intermediate cylinder moves downwardly, said intermediate cylinder having means at its upper end sealingly engaging the interior of the outer cylinder so that the intermediate cylinder is ejected from the outer cylinder in plunger-like fashion with the fluid pressure acting on the area of the annulus between the exterior of the plunger and the interior of the outer cylinder, guiding means on the upper end of the intermediate cylinder engaging the plunger to maintain a concentric relation between such upper end and said plunger, said guiding means providing for the flow of fluid therepast between such port means and space above said packing means, and means whereby fluid under pressure may be injected into said plunger to cause said intermediate cylinder to move downwardly and then cause said intermediate cylinder and said outer cylinder to move upwardly.

5. A mast assembly comprising an extensible upright structure, a load carriage movably engaging said structure, a compound cylinder unit including an inner cylinder constituting a plunger, an intermediate cylinder and an outer cylinder, said intermediate cylinder being shorter than said inner cylinder and movable downwardly upon the application of fluid pressure to said cylinder unit, means connecting said intermediate cylinder to the load carriage to elevate the load carriage without extending the upright structure, the last-named means having a portion elevated by said outer cylinder during upward movement of said outer cylinder, said outer cylinder being engageable with said upright structure during its upward movement to extend said upright structure, said outer cylinder being subsequently movable upwardly upon continued application of pressure to raise the carriage and extend the upright structure,

said plunger having guide portions at its upper end slidably engaging the interior of said intermediate cylinder, said intermediate cylinder having guide portions at its upper end slidably engaging the exterior of said plunger, the first and second mentioned guide portions being arranged to by-pass one another during relative movement between said intermediate cylinder and said plunger.

6. A compound cylinder unit for an industrial lift truck, said unit including an inner cylinder constituting a plunger, an intermediate cylinder surrounding said plunger at the upper portion thereof in the contracted position of said compound cylinder, said intermediate cylinder being shorter than said plunger and being open at its opposite ends, an outer cylinder surrounding said intermediate cylinder and having a closed upper end above the upper ends of the plunger and intermediate cylinder, said intermediate cylinder having means projecting below the lower end of said outer cylinder for supporting reeving means, said intermediate cylinder having means at its upper end sealingly engaging the interior of the outer cylinder and means at its lower end sealingly engaging the exterior of said plunger so that the intermediate cylinder is ejected from the outer cylinder in plunger-like fashion with the fluid pressure acting on the area of the annulus between the exterior of the plunger and the interior of the outer cylinder, guiding means on the upper end of the intermediate cylinder engaging the plunger to maintain a concentric relation between such upper end and said plunger, said guiding means providing for the flow of fluid therepast between such port means and space above said packing means, and means whereby fluid under pressure may be injected into said plunger to cause said intermediate cylinder to move downwardly and subsequently cause upward movement of said outer cylinder, said outer cylinder and intermediate cylinder having inter-engaging portions to enable said outer cylinder to pull said intermediate cylinder upwardly during upward movement of said outer cylinder at a time when said portions are engaged.

7. A mast assembly comprising an extensible upright structure, a load carriage movably engaging said structure, a compound ram for elevating said carriage along said upright structure without extension of said structure and then extending said structure and further elevating said carriage, said ram being extensible in the direction of extension of said upright structure, said ram comprising a plurality of telescopically-related fluidoperated members including an inner member constituting a plunger, an intermediate member of tubular form slidably engaging said plunger, and an outer member of tubular form slidably engaging said intermediate member, said outer member being shorter than said plunger and having a closed end which in the contracted condition of said ram is next to an end of said plunger, said intermediate member being open at both ends and in the contracted condition of said ram having one end adjacent the mentioned end of said outer member and having its other end projecting from the other end of said outer member, said intermediate member being shorter than said plunger to provide for movement of said intermediate member along said plunger a predetermined extent without projection of said other end of said intermediate member beyond the other end of said plunger, said intermediate member having sealing means at said other end thereof sealingly engaging said plunger and having sealing means at said one end sealingly engaging said outer member, said intermediate member having guide means at said one end thereof slidably engaging said plunger, reeving means interconnecting said load carriage and upright structure and said other end of said intermediate member to cause elevation of said carriage upon movement of said intermediate member along said plunger in a direction away from said one end of said plunger, and continued elevation of said carriage upon ejection of said plunger from said intermediate and outer members, means whereby ejection of said plunger causes extension of said upright structure, and means for supplying fluid under pressure to said ram to cause the above movements, the intermediate member having a lighter load in relation to its effective surface area than said plunger so that said intermediate member moves first.

References Cited in the file of this patent UNITED STATES PATENTS Schroeder Apr. 25, 1950 Quayle Aug. 8, 1950 Lawless May 6, 1952 Shaifer Mar. 2, 1954 FOREIGN PATENTS France Feb. 16, 1955 (Addition) 

1. A MAST ASSEMBLY COMPRISING AN EXTENSIBLE UPRIGHT STRUCTURE, A LOAD CARRIAGE MOVABLE ENGAGING SAID STRUCTURE, A COMPOUND CYLINDER UNIT INCLUDING AN INNER CYLINDER CONSTITUTING A PLUNGER, AN INTERMEDIATE CYLINDER AND AN OUTER CYLINDER, SAID INTERMEDIATE CYLINDER BEING SHORTER THAN SAID INNER CYLINDER AND MOVABLE DOWNWARDLY UPON THE APPLICATION OF FLUID PRESSURE TO SAID CYLINDER UNIT, MEANS CONNECTING SAID INTERMEDIATE CYLINDER TO THE LOAD CARRIAGE TO ELEVATE THE LOAD CARRIAGE WITHOUT EXTENDING THE UPRIGHT STRUCTURE, SAID OUTER CYLINDER BEING SUBSEQUENTLY MOVABLY UPWARDLY UPON CONTINUED APPLICATION OF PRESSURE TO RAISE THE CARRIAGE AND EXTEND THE UPRIGHT STRUCTURE, SAID PLUNGER HAVING GUIDE PORTIONS AT ITS UPPER END SLIDABLY ENGAGING THE INTERIOR OF SAID INTERMEDIATE CYLINDER, SAID INTERMEDIATE CYLINDER HAVING GUIDE PORTIONS AT ITS UPPER END SLIDABLY ENGAGING THE EXTERIOR OF SAID PLUNGER, THE FIRST AND SECOND MENTIONED GUIDE PORTIONS BEING ARRANGED TO BY-PASS ONE ANOTHER DURING RELATIVE MOVEMENT BETWEEN SAID INTERMEDIATE CYLINDER AND SAID PLUNGER. 